This invention relates to improvements in earpiece acoustics, and in particular to earpieces used in mobile telephones.
Much emphasis has recently been placed on improving the audio quality of mobile phones. This is a challenging role for the designer since the drive for smaller products is contrary to the goal of high quality audio. One of the problems in moving to smaller earpiece speakers is the loss in the low frequency output efficiency. Coupled to this, the speaker output at low frequencies (300 Hz to 1000 Hz) becomes more sensitive to the changing acoustic conditions resulting in highly variable performance between users. The primary acoustic parameter responsible for this variability in performance is termed Acoustic Leakage, and is associated with poor low frequency audio quality due to unpredictable sealing between the user""s ear and the phone""s front cover. The acoustic leak formed in this way causes the speech from the phone earpiece to sound weak and thin due to insufficient low frequency content.
Standard earpiece designs that are not leak tolerant experience large variations in audio quality due to the fluctuating acoustic loads imposed by a users ear. The result is poor low frequency audio performance which causes speech output through the earpiece to sound thin and weak. Leak tolerant designs offer a more predictable and stable audio quality across a wide range of users and operating conditions.
The most advanced leak tolerant design currently available makes the speaker less sensitive to external loading conditions by introducing a designed acoustic leak within the phone""s front cover. In practice the speaker is held a fraction of a millimeter away from the front cover and the sound energy is xe2x80x98leakedxe2x80x99 into the phone internally. This internal leak causes the speaker output at low frequencies to be less dependent on external load variations. However, this leak tolerant design is hard to realise practically.
According to the present invention, there is provided a resonator for a radiotelephone having a housing with an earpiece port and a loudspeaker, the resonator comprising a housing, a first channel for channelling sound between the loudspeaker and the earpiece port, and an internal cavity and second channel for channelling sound between the loudspeaker and the internal cavity, to provide a specified resonance performance.
The second channel and internal cavity form a Helmholtz resonator whose response is controlled by the physical dimensions of the second channel, the internal cavity and the area of the earpiece port. Hence, the present invention provides a self-contained acoustic solution for a given earpiece port. The self-contained acoustic solution is favourable for a number of reasons.
Firstly, its leak tolerant characteristics are independent of the internal characteristics of the telephone. Hence, the leak tolerant characteristics do not vary with the ageing and internal acoustics of the radiotelephone and thus this self-contained acoustic solution more reliable than existing leak-tolerant solutions. Moreover, the leak tolerance performance is phone design independent, so that the same earpiece solution can be used for a range of different phones.
Secondly, the design impedes the ingression of dirt and water into the phone. Unlike the present leak tolerant solution which requires large earpiece ports, the design of the present invention works better with small speaker ports and consequently increases speaker protection. Also, as the acoustic system is separate from the internal electronics etc. of the phone, any dirt or water which did manage to enter through the earpiece port would not reach these internal electronics and thus would not damage any sensitive electronic components.
Thirdly, there is no extra leakage of sound energy into the radiotelephone compared to non-leak tolerant phones. That is, acoustic coupling between the speaker and the microphone is the same as for a standard non-leak tolerant phone. Hence, the design according to the present invention avoids any potential unwanted acoustic coupling between the speaker and microphone which might occur in present leak-tolerant systems when sound energy from the loudspeaker is leaked into the phone.
The internal cavity of the resonator of the present invention may be exposed through an open face in the resonator housing. This open face may be closable by part of the housing of the radiotelephone, to reduce the thickness of the radiotelephone. Alternatively, the internal cavity of the resonator may be enclosed within the resonator housing, so that no design restraints are even put on the shape of the earpiece part of the radiotelephone housing.
The resonator may comprise a plurality of internal cavities and channels for channelling sound between the loudspeaker and the respective internal cavity. The choice will depend on the acoustic characteristics required in the specific application.
There is also provided an acoustic insert for a radiotelephone having a housing with an earpiece port, the insert comprising a resonator according to the present invention and loudspeaker.
The loudspeaker may have a low frequency response which complements the specified resonance performance. This would then provide a combined flat response resulting in a more stable high quality audio performance.
There is also provided a radiotelephone comprising a housing having an earpiece port, a loudspeaker, and a resonator according to the present invention. The resonator and loudspeaker may form part of an acoustic insert.
The radiotelephone preferably comprises a compensation filter for compensating for the specified resonance performance, so as to provide a combined flat response resulting in a more stable high quality audio performance. Such a compensation filter may be realised by the loudspeaker having a low frequency response which complements the specified resonance performance. Alternatively, it may be realised by a digital signal processor. This alternative is preferred since it enables the use of conventional speakers which are much cheaper than a speaker with an enhanced low-frequency response, for example.
The radiotelephone housing may form at least part of the housing of the resonator. For example, but not exclusively, it may be used to cover an open face in the resonator housing to enclose the internal cavity of the resonator.
The internal cavity or plurality of cavities may form a ring. Alternatively, the may form a square, rectangle or the like.